US20070176708A1 - Narrow impedance conversion device - Google Patents
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- US20070176708A1 US20070176708A1 US11/500,943 US50094306A US2007176708A1 US 20070176708 A1 US20070176708 A1 US 20070176708A1 US 50094306 A US50094306 A US 50094306A US 2007176708 A1 US2007176708 A1 US 2007176708A1
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- 238000006243 chemical reaction Methods 0.000 title claims abstract description 62
- 239000004020 conductor Substances 0.000 claims abstract description 221
- 230000005540 biological transmission Effects 0.000 claims abstract description 36
- 238000003780 insertion Methods 0.000 abstract description 4
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- 239000000523 sample Substances 0.000 description 13
- 230000008878 coupling Effects 0.000 description 10
- 238000010168 coupling process Methods 0.000 description 10
- 238000005859 coupling reaction Methods 0.000 description 10
- 238000002310 reflectometry Methods 0.000 description 10
- 238000005259 measurement Methods 0.000 description 8
- 101100360207 Caenorhabditis elegans rla-1 gene Proteins 0.000 description 3
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P3/00—Waveguides; Transmission lines of the waveguide type
- H01P3/02—Waveguides; Transmission lines of the waveguide type with two longitudinal conductors
- H01P3/08—Microstrips; Strip lines
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P5/00—Coupling devices of the waveguide type
- H01P5/02—Coupling devices of the waveguide type with invariable factor of coupling
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P1/00—Auxiliary devices
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P3/00—Waveguides; Transmission lines of the waveguide type
Definitions
- the present invention relates to an impedance conversion device, and in particular to an impedance conversion device that can be inserted into a stacked pair line.
- An object of the present invention is to provide an impedance conversion device that is narrow enough for insertion into a stacked pair line.
- the invented impedance conversion device comprises first, second, third, and fourth conductors, each having a first end and a second end.
- the conductors are arranged so that the first and second conductors form a first transmission line having a first characteristic impedance, the first and third conductors form a second transmission line having a second characteristic impedance different from the first characteristic impedance, the second and fourth conductors form a third transmission line having the second characteristic impedance, and the third and fourth conductors form a fourth transmission line having the first characteristic impedance.
- a first resistor having a resistance equal to the first characteristic impedance is connected between the second ends of the second and fourth conductors, which are mutually proximate.
- a second resistor having a resistance equal to the second characteristic impedance is connected between the first ends of the third and fourth conductors, which are mutually proximate.
- the four conductors transmit a signal that is input at the first ends of the first and second conductors and output at the second ends of the first and third conductors.
- the fourth conductor preferably has a length not exceeding one-fourth of the fundamental wavelength of the transmitted signal.
- the impedance of the transmitted signal is converted efficiently, and the dimensions of the impedance conversion device in the directions orthogonal to the longitudinal direction of the conductors are comparatively small, permitting the impedance converting device to be formed in a confined space and in particular to be inserted into a stacked pair line.
- Use of this impedance conversion device can contribute to a reduction in the size of microelectronic parts.
- FIG. 1 is a perspective view of an impedance conversion device embodying the present invention
- FIG. 2 is a top plan view of the impedance conversion device in FIG. 1 ;
- FIG. 3 is a bottom plan view of the impedance conversion device in FIG. 1 ;
- FIG. 4 is a side elevation view of the impedance conversion device in FIG. 1 ;
- FIG. 5 is a sectional view through line V-V in FIGS. 2-4 ;
- FIG. 6 is a sectional view through line VI-VI in FIGS. 2-4 ;
- FIG. 7 is a sectional view through line VII-VII in FIGS. 2-4 ;
- FIG. 8 is a top plan view of a structure used in time-domain reflectometry
- FIG. 9 is a bottom plan view of the structure in FIG. 8 ;
- FIG. 10 depicts a time-domain reflectometer, and a coaxial cable and probes connected thereto;
- FIG. 11 shows exemplary waveforms obtained by time-domain reflectometry using the structure in FIGS. 8 and 9 ;
- FIG. 12 schematically depicts the impedance conversion device in FIG. 1 with a direct current source connected on its input side and a load resistor connected on its output side;
- FIG. 13 schematically depicts the impedance conversion device in FIG. 1 with a pulse generator connected on its input side, a load resistor connected on its output side, and an oscilloscope connected to measure the voltage on the output side;
- FIG. 14 is a top plan view of an impedance conversion device used in time-domain reflectometry
- FIG. 15 is a bottom plan view of an impedance conversion device used in time-domain reflectometry
- FIG. 16 shows exemplary waveforms obtained with the measurement setup shown in FIG. 13 ;
- FIG. 17 shows exemplary waveforms obtained with the measurement setup shown in FIG. 13 with the output side left electrically open;
- FIG. 18 shows exemplary waveforms obtained with the measurement setup shown in FIG. 13 with the central part of the conductor lengthened
- FIG. 19 is a top plan view of another structure used in time-domain reflectometry.
- FIG. 20 is a bottom plan view of the structure in FIG. 19 ;
- FIG. 21 shows an exemplary waveform obtained by time-domain reflectometry using the structure in FIGS. 19 and 20 ;
- FIG. 22 is a perspective view illustrating crosstalk between mutually adjacent conductors
- FIG. 23 is a sectional view illustrating crosstalk between mutually adjacent conductors
- FIG. 24 is a sectional view illustrating another embodiment of the invention.
- the impedance conversion device comprises first, second, third, and fourth strip-like conductors 11 , 12 , 13 , 14 , first and second resistors 15 , 16 , and a dielectric sheet 17 .
- the first to fourth conductors 11 , 12 , 13 , 14 extend in mutually parallel straight lines.
- the dielectric sheet 17 has a first surface or upper surface 17 a (uppermost in FIGS. 1 and 4 - 7 ) and a second surface or lower surface 17 b .
- the first and third conductors 11 , 13 are disposed side by side on the upper surface 17 a of the dielectric sheet 17 , spaced apart from each other in a direction orthogonal to their lengths and parallel to the upper surface 17 a and lower surface 17 b of the dielectric sheet 17 .
- the second and fourth conductors 12 , 14 are similarly disposed side by side on the lower surface 17 b of the dielectric sheet 17 .
- the first conductor 11 and the second conductor 12 are disposed on opposite sides of the dielectric sheet 17 , facing each other in a direction orthogonal to the upper surface 17 a and lower surface 17 b of the dielectric sheet 17 .
- the third conductor 13 and the fourth conductor 14 are similarly disposed on opposite sides of the dielectric sheet 17 , facing each other.
- the impedance conversion device 1 has an input part or region 1 a , a central part or region 1 b , and an output part or region 1 c .
- the input region 1 a is the region near the input end id of the impedance conversion device 1 ; the output region 1 c is the region near the output end 1 e of the impedance conversion device 1 .
- the central region 1 b is the region between the input region 1 a and the output region 1 c .
- the input region 1 a , the central region 1 b , and the output region 1 c are mutually contiguous.
- the first conductor 11 extends across the input region 1 a , the central region 1 b , and the output region 1 c of the impedance conversion device 1 ; the first conductor 11 has an input part 11 a , a central part 11 b , and an output part 11 c disposed in the input region 1 a , the central region 1 b , and the output region 1 c , respectively.
- the second conductor 12 extends across the input region 1 a and the central region 1 b of the impedance conversion device 1 , and has an input part 12 a and a central part 12 b disposed in the input region 1 a and the central region 1 b , respectively.
- the third conductor 13 extends across the central region 1 b and the output region 1 c of the impedance conversion device 1 , and has a central part 13 b and an output part 13 c disposed in the central region 1 b and the output region 1 c , respectively.
- the fourth conductor 14 extends only across the central region 1 b , and has a central part 14 b disposed in the central region 1 b.
- the first conductor 11 and second conductor 12 form a transmission line having a first characteristic impedance z 1 .
- the second conductor 12 and fourth conductor 14 form a transmission line having a second characteristic impedance z 2 different from the first characteristic impedance z 1 .
- the first conductor 11 and the third conductor 13 form a transmission line having the second characteristic impedance z 2 .
- the third conductor 13 and the fourth conductor 14 form a transmission line having the first characteristic impedance z 1 .
- the first conductor 11 is disposed so that one end (the input end) 11 d is at the input end 1 d of the impedance conversion device 1 , and the other end (the output end) 11 e is at the output end of the impedance conversion device 1 .
- the second conductor 12 is disposed so that one end (the input end) 12 d is at the input end 1 d of the impedance conversion device 1 , and the other end (the output end) 12 e is at the boundary 1 g between the central region 1 b and the output region 1 c of the impedance conversion device 1 .
- the third conductor 13 is disposed so that one end (the input end) 13 d is at the boundary 1 f between the input region 1 a and the central region 1 b of the impedance conversion device 1 , and the other end (the output end) 13 e is at the output end 1 e of the impedance conversion device 1 .
- the fourth conductor 14 is disposed so that one end (the input end) 14 d is at the boundary 1 f between the input region 1 a and the central region 1 b of the impedance conversion device 1 , and the other end (the output end) is at the boundary 1 g between the central region 1 b and the output region 1 c of the impedance conversion device 1 .
- the output end 12 e of the second conductor 12 and the output end 14 e of the fourth conductor 14 are both disposed on the lower surface 17 b of the dielectric sheet 17 and are mutually proximate.
- the input end 13 d of the third conductor 13 and the input end 14 d of the fourth conductor 14 are disposed on the lower surface 17 b and the upper surface 17 a of the dielectric sheet 17 , respectively, and are mutually proximate.
- a first resistor 15 is mounted on the lower surface 17 b of the dielectric sheet 17 .
- the first resistor 15 interconnects the output end 12 e of the second conductor 12 and the output end 14 e of the fourth conductor 14 , and has a resistance R 1 equal to the first characteristic impedance z 1 .
- a second resistor 16 is formed so that it extends through the dielectric sheet 17 .
- the second resistor 16 interconnects the input end 13 d of the third conductor 13 and the input end 14 d of the fourth conductor 14 , and has a resistance R 2 equal to the second characteristic impedance z 2 .
- the value (the absolute value) of the first characteristic impedance z 1 is, for example, fifty ohms (50 ⁇ ), and the value (the absolute value) of the second characteristic impedance z 2 is, for example, 82 ⁇ .
- the first to fourth conductors 11 to 14 have identical cross-sectional configurations, for example, a thickness (the vertical dimension in FIGS. 5-7 ) of 40 micrometers, and a width (the horizontal dimension in FIGS. 5-7 ) of 0.8 millimeters. (The dimensions in the drawings are not shown proportional to the actual dimensions.)
- the dielectric sheet 17 has a thickness of 170 micrometers; the distance between the first conductor 11 and the second conductor 12 and the distance between the third conductor 13 and the fourth conductor 14 are equal to the thickness of the dielectric sheet 17 .
- the distance between the first conductor 11 and the third conductor 13 and the distance between the second conductor 12 and the fourth conductor 14 are identically 100 micrometers (0.1 millimeters).
- the first to fourth conductors parallel each other in the central region 1 b , which therefore may be referred to as the ‘quadri-parallel’ part below.
- the input region 1 a and the output region 1 c may be referred to as ‘duo-parallel’ parts, as only the first and second conductors 11 and 12 are parallel in the input region 1 a , and only the first and third conductors 11 and 13 are parallel in the output region 1 c.
- the length of the central region 1 b of the impedance conversion device that is, the length of conductor 14 (the length in the longitudinal direction in which conductors 11 to 14 extend) preferably does not exceed one-fourth of the fundamental wavelength of the signal that is transmitted, and is preferably at least ten times as long as the larger of the two distances that separate the first conductor 11 from the second conductor 12 and the first conductor 11 from the third conductor 13 . More specifically, the length is preferably longer than 1/64 of the fundamental wavelength of the transmitted signal.
- the impedance conversion device 1 When the impedance conversion device 1 is configured as above, its input impedance Zin is equal to the first characteristic impedance z 1 (50 ⁇ ) and its output impedance Zout is equal to the second characteristic impedance z 2 (82 ⁇ ). Impedance conversion therefore takes place. This was confirmed by using TDR (time domain reflectometry) to measure the impedance of the transmission lines.
- TDR time domain reflectometry
- TDR is carried out by transmitting a pulsed signal and observing the reflection of the pulse from the circuit under test; TDR detects changes in impedance along the transmission path of the signal.
- FIGS. 8 and 9 are a top plan view and a bottom plan view of a structure used for time-domain reflectometry, corresponding respectively to FIGS. 2 and 3 .
- the structure is similar to the impedance conversion device 1 shown in FIGS. 1-7 ; a dielectric sheet 117 (corresponding to the dielectric sheet 17 in FIG. 1 ) has a first conductor 111 and a third conductor 113 mounted on its upper surface 117 a , and a second conductor 112 and a fourth conductor 114 mounted on its lower surface 117 b .
- the first to fourth conductors 111 to 114 correspond to the first to fourth conductors 11 to 14 in FIGS. 1-7 , with the same thickness and width as the first to fourth conductors.
- the first conductor 111 and the second conductor 112 face each other across the dielectric sheet 117 ; the third conductor 113 and the fourth conductor 114 face each other across the dielectric sheet 117 .
- Strip-like leads 121 to 124 formed of the same material as the conductors are mounted at the ends 111 h to 114 h of the first to fourth conductors 111 to 114 (the left ends in FIGS. 8 and 9 ); connecting pads 131 to 134 are mounted at the ends of the leads 121 to 124 .
- the length LL of the leads 121 to 124 is twelve millimeters.
- the TDR apparatus 51 had a coaxial cable 52 terminating in probes 53 a and 53 b for launching signal pulses and receiving reflected waves; the probes 53 a and 53 b were placed in contact with the conductors forming the transmission line so that signals could be input and their reflections received.
- connecting pads 131 and 132 of conductor 111 and conductor 112 were contacted by probes 53 a and 53 b ;
- connecting pads 133 and 134 of conductor 113 and conductor 114 were contacted by probes 53 a and 53 b .
- FIG. 11 Exemplary waveforms that appeared on the display of the TDR apparatus 51 are shown in FIG. 11 .
- curves B 5 a , B 5 b , B 5 c , and B 5 d indicate the waveforms obtained when conductor 111 and conductor 112 , conductor 113 and conductor 114 , conductor 111 and conductor 113 , and conductor 112 and conductor 114 , respectively, were contacted by probes 53 a and 53 b ; the zero levels of different waveforms are mutually offset for visibility.
- the leftmost regions RXa to RXd of these curves indicate the impedance of the coaxial cable 52 (50 ⁇ ); the regions adjacent to regions RXa to RXd on the right correspond to the sections in which probes 53 a and 53 b make contact with connecting pads 131 to 134 or the ends 111 i to 114 i of conductors 111 to 114 ; the central regions RPa to RPd indicate the impedance of conductors 111 to 114 (the impedance of the transmission line comprising conductors 111 and 112 , the transmission line comprising conductors 113 and 114 , the transmission line comprising conductors 111 and 113 , and the transmission line comprising conductors 112 and 114 ); and the rightmost regions ROa to ROd indicate the impedance at the electrically open ends.
- Regions RLa and RLb of curves B 5 a and B 5 b which are between the central regions RPa and RPb and the regions RCa to RCd corresponding to the contact sections of probes 53 a and 53 b , indicate the impedance of the leads 121 to 124 ; regions RLc and RLd of curves B 5 c and B 5 d , which are between the central regions RPc and RPd and the regions ROc and ROd corresponding to the electrically open ends, indicate the impedance of the leads 121 to 124 .
- Table 1 The values shown in Table 1 can be read from the measured waveforms as the impedance of each pair of conductors.
- the impedance conversion efficiency and waveform distortion of the novel impedance conversion device 1 were studied under various conditions.
- a load resistor 18 with a value equal to the second characteristic impedance z 2 (82 ⁇ ) was connected between the output ends of the impedance conversion device 1 , that is, between the output ends 11 e and 13 e of conductors 11 and 13 , as shown in FIG. 12 .
- conductors 11 to 14 are shown as coplanar to simplify the depiction of their electrical connection relationships and the depiction of resistors 15 and 16 is also simplified.
- V out V in ⁇ R 2/(2 ⁇ R 2+ R 1+ R in) ⁇
- Rin is the internal resistance of the direct current source 60 .
- V out V in ⁇ R 2/(2 ⁇ R 2+2 ⁇ R 1) ⁇ (1)
- the experimental impedance conversion device 1 shown in FIGS. 14 and 15 was used in this measurement.
- the experimental device 1 shown in FIGS. 14 and 15 is substantially the same as the impedance conversion device 1 shown in FIGS. 1-7 , but has leads 121 and 122 disposed at the input ends 11 d and 12 d of conductors 11 and 12 and connecting pads 131 and 132 disposed at the ends of leads 121 and 122 , similar to the structure shown in FIGS. 8 and 9 .
- the dielectric sheet 17 extends farther than in FIGS. 1-7 .
- the probes 63 a and 63 b of the pulse generator 61 were placed in contact with the connecting pads 131 and 132 on the input side.
- An oscilloscope 65 having high-impedance differential probes 66 a and 66 b was used. The measured waveforms are shown in FIG. 16 .
- curves B 6 a , B 6 b , B 6 c , B 6 d , and B 6 e indicate waveforms obtained when the amplitude of the supplied pulses was 500 mV and the frequency of the pulse train was 100 MHz, 500 MHz, 1 GHz, 2 GHz, and 3 GHz, respectively.
- the wave height values and rise times (the time required for the voltage level to increase from 20 percent to 80 percent of the wave height) determined from the measured waveforms are shown in Table 2.
- the measured wave height was 255.1 mV.
- FIG. 18 shows the measured waveforms for another experimental device in which the central part had a length of twenty millimeters.
- waveforms B 8 a , B 8 b , B 8 c , B 8 d , and B 8 e were obtained with pulse train frequencies of 100 MHz, 500 MHz, 12 GHz, 2 GHz, and 3 GHz, respectively.
- the wave height values determined from the measured waveforms are shown in Table 4.
- FIG. 18 and Table 4 show a decrease in voltage and an increase in waveform distortion. The reason is thought to be the long distance between boundaries 1 f and 1 g , which causes a relatively long elapse of time from reflection at one boundary to reflection at the other boundary, leading to multiple reflections that distort the waveforms.
- the characteristic impedance of the duo-parallel parts 1 a and 1 c and the characteristic impedance of the quadri-parallel part 1 b are slightly different. Multiple reflections therefore occur.
- the quadri-parallel part should have a length not exceeding one-fourth of the fundamental wavelength of the signal that is transmitted. If the specific inductive capacity of the transmission line is four, then the electromagnetic wave speed is 1.5 ⁇ 10 8 m/s, and if the frequency of the pulse train supplied from the pulse generator 61 is 3 GHz, it follows that the wavelength is 50 millimeters, one-fourth of which is 12.5 millimeters.
- the length of the quadri-parallel part 1 b need only be sufficient for electromagnetic waves to reshape the electromagnetic space between the parallel conductors. Interference between the conductors is caused by the spreading of the electromagnetic waves in a direction orthogonal to their direction of propagation, and the spreading speed is the same as the speed with which the electromagnetic waves propagate along the transmission line.
- Reshaping of the electromagnetic space is possible if an electromagnetic wave can travel back and forth between the conductors about five times; the length corresponding to the delay time is a length ten times as long as the larger of the two distances separating the conductors (the larger of the distance (170 micrometers) between the first conductor 11 and the second conductor 12 and the distance (100 micrometers or 0.1 millimeter) between the first conductor 11 and the third conductor 13 ).
- the larger of the two distances between the conductors is 170 micrometers, ten times that length is 1.7 millimeters; the quadri-parallel structure is effective if its length is equal to or greater than this value.
- FIGS. 19 and 20 show the structure used in this time-domain reflectometry experiment.
- the structure shown in FIGS. 8 and 9 was further modified by removing the parts near the ends 113 i and 114 i of the third conductor 113 and the fourth conductor 114 .
- the length LS of the removed parts was 25 millimeters; the section with the removed parts constituted the duo-parallel part.
- Connecting pads 131 and 132 of the first conductor 111 and the second conductor 112 of this structure were contacted by probes 53 a and 53 b of the TDR apparatus 51 .
- the measured waveforms are shown in FIG. 21 .
- the longitudinal axis in FIG. 21 is enlarged compared to that in FIG. 11 .
- region RXa corresponds to a section of the coaxial cable 52
- region RCa corresponds to leads 121 and 122
- region RPa 1 corresponds to the quadri-parallel part (length LD)
- region RPa 2 corresponds to the duo-parallel part (length LS)
- region ROa corresponds to the electrically open ends.
- the impedance of the quadri-parallel part (length LD) shown in FIG. 21 is 48 ⁇ , and the impedance of the right-side region RPa 22 (excluding the region RPa 21 adjacent to the region RPa 1 corresponding to the quadri-parallel part) of the duo-parallel part (length LS) is 51.2 ⁇ ; reflection occurs due to this difference.
- the upper limit described above on the length of the quadri-parallel part 1 b is set in order to prevent reflection from occurring repeatedly and leading to multiple reflections.
- the characteristic impedance changes gradually in the region RPa 21 adjacent to the region RPa 1 corresponding to the quadri-parallel part.
- This part corresponds to 125 picoseconds of time, which is the sum of the slump due to the rise time of the step waveform of the TDR apparatus 51 (35 picoseconds, the same as the slump at the contact section RCa and the electrically open end ROa) and the time taken to detect the change; these factors cannot be separated accurately, but the physical phenomena that operate during detection are similar to the reshaping of the electromagnetic space described above.
- the pulse energy input to one of the parallel conductors 11 to 14 causes various combinations of interference on adjacent conductors; the optimal state is ultimately the one in which inverted waveform energy is induced in the proximate conductors by electromagnetic interference as shown in FIG. 23 , with the crosstalk energy corresponding to the electromagnetic dispersion energy. This is in forward waves. Though backward waves are also induced, they are omitted here.
- the input induces vertical coupling (coupling between the vertically adjacent conductors 11 and 12 in FIG. 1 ), and so the upper-left conductor becomes the output of the adjacent vertical coupling. With horizontal coupling (coupling between the horizontally adjacent conductors in FIG.
- the conductors are disposed on the upper surface and lower surface of the dielectric sheet in FIGS. 1-7 , a structure in which conductors 11 to 14 are all embedded in a dielectric material 21 as shown in FIG. 24 (a sectional view similar to FIG. 6 ) is also possible.
- the first to fourth conductors 11 to 14 may be formed in the same way as two pairs of stacked pair conductors are formed.
- the first to third conductors 11 to 13 have input parts 11 a and 12 a and output parts 11 c and 13 c as well as central parts 11 b , 12 b , and 13 b , but the impedance conversion device may comprise only the central parts; the input parts 11 a and 12 a and output parts 11 c and 13 c may be omitted.
- first to fourth conductors 11 to 14 extend in straight lines in the above embodiment, they may be curved.
- the cross-sectional shapes and dimensions of the first to fourth conductors 11 to 14 need not all be the same; some may differ from the others.
Abstract
Description
- 1. Field of the Invention
- The present invention relates to an impedance conversion device, and in particular to an impedance conversion device that can be inserted into a stacked pair line.
- 2. Description of the Related Art
- An example of a conventional impedance conversion device that can be inserted in a transmission line is given in Japanese Patent Application Publication No. 10-224123. The disclosed device is designed for insertion into a microstrip line, however, and is too wide in the direction orthogonal to the line for insertion into a stacked pair line.
- An object of the present invention is to provide an impedance conversion device that is narrow enough for insertion into a stacked pair line.
- The invented impedance conversion device comprises first, second, third, and fourth conductors, each having a first end and a second end. The conductors are arranged so that the first and second conductors form a first transmission line having a first characteristic impedance, the first and third conductors form a second transmission line having a second characteristic impedance different from the first characteristic impedance, the second and fourth conductors form a third transmission line having the second characteristic impedance, and the third and fourth conductors form a fourth transmission line having the first characteristic impedance.
- A first resistor having a resistance equal to the first characteristic impedance is connected between the second ends of the second and fourth conductors, which are mutually proximate. A second resistor having a resistance equal to the second characteristic impedance is connected between the first ends of the third and fourth conductors, which are mutually proximate.
- The four conductors transmit a signal that is input at the first ends of the first and second conductors and output at the second ends of the first and third conductors. The fourth conductor preferably has a length not exceeding one-fourth of the fundamental wavelength of the transmitted signal.
- The impedance of the transmitted signal is converted efficiently, and the dimensions of the impedance conversion device in the directions orthogonal to the longitudinal direction of the conductors are comparatively small, permitting the impedance converting device to be formed in a confined space and in particular to be inserted into a stacked pair line. Use of this impedance conversion device can contribute to a reduction in the size of microelectronic parts.
- In the attached drawings:
-
FIG. 1 is a perspective view of an impedance conversion device embodying the present invention; -
FIG. 2 is a top plan view of the impedance conversion device inFIG. 1 ; -
FIG. 3 is a bottom plan view of the impedance conversion device inFIG. 1 ; -
FIG. 4 is a side elevation view of the impedance conversion device inFIG. 1 ; -
FIG. 5 is a sectional view through line V-V inFIGS. 2-4 ; -
FIG. 6 is a sectional view through line VI-VI inFIGS. 2-4 ; -
FIG. 7 is a sectional view through line VII-VII inFIGS. 2-4 ; -
FIG. 8 is a top plan view of a structure used in time-domain reflectometry; -
FIG. 9 is a bottom plan view of the structure inFIG. 8 ; -
FIG. 10 depicts a time-domain reflectometer, and a coaxial cable and probes connected thereto; -
FIG. 11 shows exemplary waveforms obtained by time-domain reflectometry using the structure inFIGS. 8 and 9 ; -
FIG. 12 schematically depicts the impedance conversion device inFIG. 1 with a direct current source connected on its input side and a load resistor connected on its output side; -
FIG. 13 schematically depicts the impedance conversion device inFIG. 1 with a pulse generator connected on its input side, a load resistor connected on its output side, and an oscilloscope connected to measure the voltage on the output side; -
FIG. 14 is a top plan view of an impedance conversion device used in time-domain reflectometry; -
FIG. 15 is a bottom plan view of an impedance conversion device used in time-domain reflectometry; -
FIG. 16 shows exemplary waveforms obtained with the measurement setup shown inFIG. 13 ; -
FIG. 17 shows exemplary waveforms obtained with the measurement setup shown inFIG. 13 with the output side left electrically open; -
FIG. 18 shows exemplary waveforms obtained with the measurement setup shown inFIG. 13 with the central part of the conductor lengthened; -
FIG. 19 is a top plan view of another structure used in time-domain reflectometry; -
FIG. 20 is a bottom plan view of the structure inFIG. 19 ; -
FIG. 21 shows an exemplary waveform obtained by time-domain reflectometry using the structure inFIGS. 19 and 20 ; -
FIG. 22 is a perspective view illustrating crosstalk between mutually adjacent conductors; -
FIG. 23 is a sectional view illustrating crosstalk between mutually adjacent conductors; -
FIG. 24 is a sectional view illustrating another embodiment of the invention. - An impedance conversion device embodying the invention will now be described with reference to the attached drawings, in which like elements are indicated by like reference characters.
- As shown in
FIGS. 1-7 , the impedance conversion device comprises first, second, third, and fourth strip-like conductors second resistors dielectric sheet 17. The first tofourth conductors - The
dielectric sheet 17 has a first surface orupper surface 17 a (uppermost in FIGS. 1 and 4-7) and a second surface orlower surface 17 b. The first andthird conductors upper surface 17 a of thedielectric sheet 17, spaced apart from each other in a direction orthogonal to their lengths and parallel to theupper surface 17 a andlower surface 17 b of thedielectric sheet 17. The second andfourth conductors lower surface 17 b of thedielectric sheet 17. - The
first conductor 11 and thesecond conductor 12 are disposed on opposite sides of thedielectric sheet 17, facing each other in a direction orthogonal to theupper surface 17 a andlower surface 17 b of thedielectric sheet 17. Thethird conductor 13 and thefourth conductor 14 are similarly disposed on opposite sides of thedielectric sheet 17, facing each other. - As shown in
FIGS. 2-4 , the impedance conversion device 1 has an input part orregion 1 a, a central part orregion 1 b, and an output part orregion 1 c. Theinput region 1 a is the region near the input end id of the impedance conversion device 1; theoutput region 1 c is the region near theoutput end 1 e of the impedance conversion device 1. Thecentral region 1 b is the region between theinput region 1 a and theoutput region 1 c. Theinput region 1 a, thecentral region 1 b, and theoutput region 1 c are mutually contiguous. - The
first conductor 11 extends across theinput region 1 a, thecentral region 1 b, and theoutput region 1 c of the impedance conversion device 1; thefirst conductor 11 has aninput part 11 a, acentral part 11 b, and anoutput part 11 c disposed in theinput region 1 a, thecentral region 1 b, and theoutput region 1 c, respectively. - The
second conductor 12 extends across theinput region 1 a and thecentral region 1 b of the impedance conversion device 1, and has aninput part 12 a and acentral part 12 b disposed in theinput region 1 a and thecentral region 1 b, respectively. - The
third conductor 13 extends across thecentral region 1 b and theoutput region 1 c of the impedance conversion device 1, and has acentral part 13 b and anoutput part 13 c disposed in thecentral region 1 b and theoutput region 1 c, respectively. - The
fourth conductor 14 extends only across thecentral region 1 b, and has acentral part 14 b disposed in thecentral region 1 b. - The
first conductor 11 andsecond conductor 12 form a transmission line having a first characteristic impedance z1. - The
second conductor 12 andfourth conductor 14 form a transmission line having a second characteristic impedance z2 different from the first characteristic impedance z1. - The
first conductor 11 and thethird conductor 13 form a transmission line having the second characteristic impedance z2. - The
third conductor 13 and thefourth conductor 14 form a transmission line having the first characteristic impedance z1. - The
first conductor 11 is disposed so that one end (the input end) 11 d is at theinput end 1 d of the impedance conversion device 1, and the other end (the output end) 11 e is at the output end of the impedance conversion device 1. - The
second conductor 12 is disposed so that one end (the input end) 12 d is at theinput end 1 d of the impedance conversion device 1, and the other end (the output end) 12 e is at theboundary 1 g between thecentral region 1 b and theoutput region 1 c of the impedance conversion device 1. - The
third conductor 13 is disposed so that one end (the input end) 13 d is at theboundary 1 f between theinput region 1 a and thecentral region 1 b of the impedance conversion device 1, and the other end (the output end) 13 e is at theoutput end 1 e of the impedance conversion device 1. - The
fourth conductor 14 is disposed so that one end (the input end) 14 d is at theboundary 1 f between theinput region 1 a and thecentral region 1 b of the impedance conversion device 1, and the other end (the output end) is at theboundary 1 g between thecentral region 1 b and theoutput region 1 c of the impedance conversion device 1. - The
output end 12 e of thesecond conductor 12 and theoutput end 14 e of thefourth conductor 14 are both disposed on thelower surface 17 b of thedielectric sheet 17 and are mutually proximate. Theinput end 13 d of thethird conductor 13 and theinput end 14 d of thefourth conductor 14 are disposed on thelower surface 17 b and theupper surface 17 a of thedielectric sheet 17, respectively, and are mutually proximate. - A
first resistor 15 is mounted on thelower surface 17 b of thedielectric sheet 17. Thefirst resistor 15 interconnects theoutput end 12 e of thesecond conductor 12 and theoutput end 14 e of thefourth conductor 14, and has a resistance R1 equal to the first characteristic impedance z1. - A
second resistor 16 is formed so that it extends through thedielectric sheet 17. Thesecond resistor 16 interconnects theinput end 13 d of thethird conductor 13 and theinput end 14 d of thefourth conductor 14, and has a resistance R2 equal to the second characteristic impedance z2. - The value (the absolute value) of the first characteristic impedance z1 is, for example, fifty ohms (50Ω), and the value (the absolute value) of the second characteristic impedance z2 is, for example, 82Ω.
- The first to
fourth conductors 11 to 14 have identical cross-sectional configurations, for example, a thickness (the vertical dimension inFIGS. 5-7 ) of 40 micrometers, and a width (the horizontal dimension inFIGS. 5-7 ) of 0.8 millimeters. (The dimensions in the drawings are not shown proportional to the actual dimensions.) - The
dielectric sheet 17 has a thickness of 170 micrometers; the distance between thefirst conductor 11 and thesecond conductor 12 and the distance between thethird conductor 13 and thefourth conductor 14 are equal to the thickness of thedielectric sheet 17. - The distance between the
first conductor 11 and thethird conductor 13 and the distance between thesecond conductor 12 and thefourth conductor 14 are identically 100 micrometers (0.1 millimeters). - The first to fourth conductors parallel each other in the
central region 1 b, which therefore may be referred to as the ‘quadri-parallel’ part below. In contrast, theinput region 1 a and theoutput region 1 c may be referred to as ‘duo-parallel’ parts, as only the first andsecond conductors input region 1 a, and only the first andthird conductors output region 1 c. - The length of the
central region 1 b of the impedance conversion device, that is, the length of conductor 14 (the length in the longitudinal direction in whichconductors 11 to 14 extend) preferably does not exceed one-fourth of the fundamental wavelength of the signal that is transmitted, and is preferably at least ten times as long as the larger of the two distances that separate thefirst conductor 11 from thesecond conductor 12 and thefirst conductor 11 from thethird conductor 13. More specifically, the length is preferably longer than 1/64 of the fundamental wavelength of the transmitted signal. - When the impedance conversion device 1 is configured as above, its input impedance Zin is equal to the first characteristic impedance z1 (50Ω) and its output impedance Zout is equal to the second characteristic impedance z2 (82Ω). Impedance conversion therefore takes place. This was confirmed by using TDR (time domain reflectometry) to measure the impedance of the transmission lines.
- TDR is carried out by transmitting a pulsed signal and observing the reflection of the pulse from the circuit under test; TDR detects changes in impedance along the transmission path of the signal.
-
FIGS. 8 and 9 are a top plan view and a bottom plan view of a structure used for time-domain reflectometry, corresponding respectively toFIGS. 2 and 3 . The structure is similar to the impedance conversion device 1 shown inFIGS. 1-7 ; a dielectric sheet 117 (corresponding to thedielectric sheet 17 inFIG. 1 ) has afirst conductor 111 and athird conductor 113 mounted on itsupper surface 117 a, and asecond conductor 112 and afourth conductor 114 mounted on itslower surface 117 b. The first tofourth conductors 111 to 114 correspond to the first tofourth conductors 11 to 14 inFIGS. 1-7 , with the same thickness and width as the first to fourth conductors. Thefirst conductor 111 and thesecond conductor 112 face each other across thedielectric sheet 117; thethird conductor 113 and thefourth conductor 114 face each other across thedielectric sheet 117.Resistors fourth conductors 111 to 114 are of equal length (LT=80 millimeters). - Strip-
like leads 121 to 124 formed of the same material as the conductors are mounted at theends 111 h to 114 h of the first tofourth conductors 111 to 114 (the left ends inFIGS. 8 and 9 ); connectingpads 131 to 134 are mounted at the ends of theleads 121 to 124. The length LL of theleads 121 to 124 is twelve millimeters. - Measurements were made of the impedance of each of the transmission lines formed by
conductor 111 andconductor 112,conductor 112 andconductor 114,conductor 113 andconductor 114, andconductor 111 andconductor 113. As shown inFIG. 10 , theTDR apparatus 51 had acoaxial cable 52 terminating inprobes probes - Specifically, to measure the impedance of the transmission line formed by
conductor 111 andconductor 112, connectingpads conductor 111 andconductor 112 were contacted byprobes conductor 113 andconductor 114, connectingpads conductor 113 andconductor 114 were contacted byprobes conductor 111 andconductor 113, the other ends 111 i and 113 i ofconductor 111 andconductor 113 were contacted byprobes conductor 112 andconductor 114, the other ends 112 i and 114 i ofconductor 112 andconductor 114 were contacted byprobes - Exemplary waveforms that appeared on the display of the
TDR apparatus 51 are shown inFIG. 11 . InFIG. 11 , curves B5 a, B5 b, B5 c, and B5 d indicate the waveforms obtained whenconductor 111 andconductor 112,conductor 113 andconductor 114,conductor 111 andconductor 113, andconductor 112 andconductor 114, respectively, were contacted byprobes - The leftmost regions RXa to RXd of these curves indicate the impedance of the coaxial cable 52 (50Ω); the regions adjacent to regions RXa to RXd on the right correspond to the sections in which probes 53 a and 53 b make contact with connecting
pads 131 to 134 or theends 111 i to 114 i ofconductors 111 to 114; the central regions RPa to RPd indicate the impedance ofconductors 111 to 114 (the impedance of the transmissionline comprising conductors line comprising conductors line comprising conductors line comprising conductors 112 and 114); and the rightmost regions ROa to ROd indicate the impedance at the electrically open ends. Regions RLa and RLb of curves B5 a and B5 b, which are between the central regions RPa and RPb and the regions RCa to RCd corresponding to the contact sections ofprobes leads 121 to 124; regions RLc and RLd of curves B5 c and B5 d, which are between the central regions RPc and RPd and the regions ROc and ROd corresponding to the electrically open ends, indicate the impedance of theleads 121 to 124. - The values shown in Table 1 can be read from the measured waveforms as the impedance of each pair of conductors.
-
TABLE 1 Conductor Pair Impedance 111, 112 49.0 Ω 113, 114 49.1 Ω 111, 113 82.0 Ω 112, 114 77.6 Ω - The impedance conversion efficiency and waveform distortion of the novel impedance conversion device 1 were studied under various conditions.
- In the first case studied, a
load resistor 18 with a value equal to the second characteristic impedance z2 (82Ω) was connected between the output ends of the impedance conversion device 1, that is, between the output ends 11 e and 13 e ofconductors FIG. 12 . InFIG. 12 ,conductors 11 to 14 are shown as coplanar to simplify the depiction of their electrical connection relationships and the depiction ofresistors - When a direct current voltage Vin is supplied from a direct
current source 60 to the input end of the impedance conversion device 1 inFIGS. 1-7 , that is, the input ends 11 d and 12 d ofconductors FIG. 12 , (electromagnetic coupling amongconductors 11 to 14 may be ignored in this case), the voltage Vout that appears across the output ends 11 e and 13 e is given by the following equation: -
Vout=Vin×{R2/(2×R2+R1+Rin)} - where Rin is the internal resistance of the direct
current source 60. - The internal resistance Rin is generally made equal to the input impedance R1; when Rin=R1, the above equation becomes:
-
Vout=Vin×{R2/(2×R2+2×R1)} (1) - If R1=50Ω and R2=82Ω, then:
-
- If the value of Vin is five hundred millivolts (500 mV), then:
-
Vout=500×82/264=155 mV (3) - Next, the voltage that appeared at the output end when a voltage pulse train was applied from a
pulse generator 61 to the input end of the impedance conversion device 1 inFIGS. 1-7 , as shown inFIG. 13 , was observed using anoscilloscope 65. InFIG. 13 ,conductors 11 to 14 are shown as being coplanar andresistors FIG. 12 . - The experimental impedance conversion device 1 shown in
FIGS. 14 and 15 was used in this measurement. The experimental device 1 shown inFIGS. 14 and 15 is substantially the same as the impedance conversion device 1 shown inFIGS. 1-7 , but has leads 121 and 122 disposed at the input ends 11 d and 12 d ofconductors pads leads FIGS. 8 and 9 . Thedielectric sheet 17 extends farther than inFIGS. 1-7 . - Measurements were made by connecting
resistors FIG. 13 , in the same way as described with reference toFIGS. 1-7 ; aload resistor 18 having a resistance (RL) equal to the second characteristic impedance z2 (82Ω) was connected across the output ends (load ends) 11 e and 13 e ofconductors central parts conductors - A
pulse generator 61 having an internal resistance Rin equal to the first impedance z1 (50Ω) and was used. Theprobes pulse generator 61 were placed in contact with the connectingpads oscilloscope 65 having high-impedance differential probes 66 a and 66 b was used. The measured waveforms are shown inFIG. 16 . - In
FIG. 16 , curves B6 a, B6 b, B6 c, B6 d, and B6 e indicate waveforms obtained when the amplitude of the supplied pulses was 500 mV and the frequency of the pulse train was 100 MHz, 500 MHz, 1 GHz, 2 GHz, and 3 GHz, respectively. - The wave height values and rise times (the time required for the voltage level to increase from 20 percent to 80 percent of the wave height) determined from the measured waveforms are shown in Table 2.
-
TABLE 2 Input frequency Wave height (mV) Rise time (ps) 500 MHz 255.1 67.3 1 GHz 222.2 53.1 2 GHz 255.1 66.5 3 GHz 259.2 59.5 - The difference between the wave height values obtained experimentally and the value obtained from equation (3) (the value of the output voltage when direct current is applied) is due to electromagnetic coupling in the transmission line.
- For example, when the frequency is 500 MHz, the measured wave height was 255.1 mV. The difference between this value and the value obtained from equation (3) (255.1 mV−155 mV=100.1 mV) represents a voltage component induced by electromagnetic coupling, and indicates that impedance conversion has been carried out effectively.
- Next, similar measurements were made with the output ends of the impedance conversion device 1, more specifically the output ends 11 e and 13 e of
conductors load resistor 18 was omitted. The measured waveforms are shown inFIG. 17 . The wave height values determined from the measured waveforms are shown in Table 3. -
TABLE 3 Input frequency Wave height (mV) 100 MHz 880 500 MHz 880.1 1 GHz 537.9 2 GHz 391.2 3 GHz 619.3 - As shown in
FIG. 17 and Table 3, the voltage level becomes higher when output ends 11 e and 13 e are left electrically open. Even when the output ends are left electrically open so that the circuit has no direct current connection, adequate energy is transmitted to the output ends ofconductors - When the output ends 11 e and 13 e of the impedance conversion device 1 are connected to a CMOS circuit gate, they are in nearly the same state as when left electrically open, so presumably the results will be nearly the same as shown in
FIG. 17 and Table 3. - Though the resistor 16 (R2=50Ω) connected between
conductors FIG. 21 . - In the above examples (
FIGS. 16 and 17 ), the central part had a length of two millimeters;FIG. 18 shows the measured waveforms for another experimental device in which the central part had a length of twenty millimeters. InFIG. 18 , waveforms B8 a, B8 b, B8 c, B8 d, and B8 e were obtained with pulse train frequencies of 100 MHz, 500 MHz, 12 GHz, 2 GHz, and 3 GHz, respectively. The wave height values determined from the measured waveforms are shown in Table 4. -
TABLE 4 Input frequency Wave height (mV) 500 MHz 311.0 1 GHz 244.8 2 GHz 397.0 3 GHz 251.4 -
FIG. 18 and Table 4 show a decrease in voltage and an increase in waveform distortion. The reason is thought to be the long distance betweenboundaries - As described above, the characteristic impedance of the duo-
parallel parts parallel part 1 b are slightly different. Multiple reflections therefore occur. In order to avoid multiple reflection resonance, the quadri-parallel part should have a length not exceeding one-fourth of the fundamental wavelength of the signal that is transmitted. If the specific inductive capacity of the transmission line is four, then the electromagnetic wave speed is 1.5×108 m/s, and if the frequency of the pulse train supplied from thepulse generator 61 is 3 GHz, it follows that the wavelength is 50 millimeters, one-fourth of which is 12.5 millimeters. - The length of the quadri-
parallel part 1 b need only be sufficient for electromagnetic waves to reshape the electromagnetic space between the parallel conductors. Interference between the conductors is caused by the spreading of the electromagnetic waves in a direction orthogonal to their direction of propagation, and the spreading speed is the same as the speed with which the electromagnetic waves propagate along the transmission line. Reshaping of the electromagnetic space is possible if an electromagnetic wave can travel back and forth between the conductors about five times; the length corresponding to the delay time is a length ten times as long as the larger of the two distances separating the conductors (the larger of the distance (170 micrometers) between thefirst conductor 11 and thesecond conductor 12 and the distance (100 micrometers or 0.1 millimeter) between thefirst conductor 11 and the third conductor 13). Thus, if the larger of the two distances between the conductors is 170 micrometers, ten times that length is 1.7 millimeters; the quadri-parallel structure is effective if its length is equal to or greater than this value. - The characteristic impedance of the quadri-
parallel part 1 b and the characteristic impedance of the duo-parallel part FIGS. 19 and 20 show the structure used in this time-domain reflectometry experiment. The structure shown inFIGS. 8 and 9 was further modified by removing the parts near theends third conductor 113 and thefourth conductor 114. The length LS of the removed parts was 25 millimeters; the section with the removed parts constituted the duo-parallel part. The remaining section (the section with no parts removed), which had a length LD of 55 millimeters, constituted the quadri-parallel part.Connecting pads first conductor 111 and thesecond conductor 112 of this structure were contacted byprobes TDR apparatus 51. The measured waveforms are shown inFIG. 21 . The longitudinal axis inFIG. 21 is enlarged compared to that inFIG. 11 . - In
FIG. 21 , region RXa corresponds to a section of thecoaxial cable 52, region RCa corresponds to leads 121 and 122, region RPa1 corresponds to the quadri-parallel part (length LD), region RPa2 corresponds to the duo-parallel part (length LS), and region ROa corresponds to the electrically open ends. - The impedance of the quadri-parallel part (length LD) shown in
FIG. 21 is 48Ω, and the impedance of the right-side region RPa22 (excluding the region RPa21 adjacent to the region RPa1 corresponding to the quadri-parallel part) of the duo-parallel part (length LS) is 51.2Ω; reflection occurs due to this difference. The upper limit described above on the length of the quadri-parallel part 1 b is set in order to prevent reflection from occurring repeatedly and leading to multiple reflections. - In the region RPa2 corresponding to the duo-parallel part, the characteristic impedance changes gradually in the region RPa21 adjacent to the region RPa1 corresponding to the quadri-parallel part. This part corresponds to 125 picoseconds of time, which is the sum of the slump due to the rise time of the step waveform of the TDR apparatus 51 (35 picoseconds, the same as the slump at the contact section RCa and the electrically open end ROa) and the time taken to detect the change; these factors cannot be separated accurately, but the physical phenomena that operate during detection are similar to the reshaping of the electromagnetic space described above.
- Next, electromagnetic coupling between the conductors, in other words, crosstalk, will be described with reference to
FIGS. 22 and 23 . - As shown in
FIG. 22 , the pulse energy input to one of theparallel conductors 11 to 14 causes various combinations of interference on adjacent conductors; the optimal state is ultimately the one in which inverted waveform energy is induced in the proximate conductors by electromagnetic interference as shown inFIG. 23 , with the crosstalk energy corresponding to the electromagnetic dispersion energy. This is in forward waves. Though backward waves are also induced, they are omitted here. The input induces vertical coupling (coupling between the verticallyadjacent conductors FIG. 1 ), and so the upper-left conductor becomes the output of the adjacent vertical coupling. With horizontal coupling (coupling between the horizontally adjacent conductors inFIG. 1 ), however, the energy becomes the sum of the original energy on one side and the energy of the far end composite wave (upper right); a voltage of 250 mV was obtained experimentally, which is larger than the divided direct current voltage of 155 mV. The difference represents an improvement in the efficiency of impedance conversion. This energy state between parallel conductors is achieved if a relationship corresponding to the one shown inFIGS. 22 and 23 is formed for even an instant (the time during which interference occurs at the speed of light); the minimum length is thus the length described above. - Though the conductors are disposed on the upper surface and lower surface of the dielectric sheet in
FIGS. 1-7 , a structure in whichconductors 11 to 14 are all embedded in adielectric material 21 as shown inFIG. 24 (a sectional view similar toFIG. 6 ) is also possible. The first tofourth conductors 11 to 14 may be formed in the same way as two pairs of stacked pair conductors are formed. - In the above embodiment, the first to
third conductors 11 to 13 haveinput parts output parts central parts input parts output parts - Although the first to
fourth conductors 11 to 14 extend in straight lines in the above embodiment, they may be curved. The cross-sectional shapes and dimensions of the first tofourth conductors 11 to 14 need not all be the same; some may differ from the others. - Those skilled in the art will recognize that further variations are possible within the scope of the invention, which is defined in the appended claims.
Claims (11)
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JP2006020479A JP4073456B2 (en) | 2006-01-30 | 2006-01-30 | Impedance converter |
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Also Published As
Publication number | Publication date |
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JP4073456B2 (en) | 2008-04-09 |
KR20070078776A (en) | 2007-08-02 |
US7446625B2 (en) | 2008-11-04 |
CN101013767A (en) | 2007-08-08 |
TW200729604A (en) | 2007-08-01 |
JP2007202005A (en) | 2007-08-09 |
KR100775945B1 (en) | 2007-11-13 |
CN100555742C (en) | 2009-10-28 |
TWI318807B (en) | 2009-12-21 |
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